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From |
"rengaweoj" <wagnerj@edc.pitt.edu> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: comparison between a repeated ordinal measures |

Date |
Wed, 30 Mar 2005 13:40:18 -0000 |

Thank you for your response. My data is in -wide- format. In order to use -ologit- or -gllamm-, does my data necessarily need to be in -long- format? I am guessing that either I need to or I have set up -ologit- and -gologit- incorrectly since the coefficient and p-value I get are quite different. Looking at the table it appears there isn't a difference between the two time points and the results I get from your programming supports this. --- In statalist@yahoogroups.com, Joseph Coveney <jcoveney@b...> wrote: > Joseph Wagner wrote > > I need to do a comparison between two ordinal measures, one at baseline > (hlths) and the other, repeated at followup(f6hlths). I have done > something similar in SAS using CATMOD. I wish to know if there has been > a change between the two time points and in which direction. > > > The data takes this form: > > > Self Rated | 6M Self Rated Health > Health | 1 2 3 4 5 | Total > -----------+--------------------------+----- > 1 | 28 18 6 0 0 | 52 > 2 | 21 78 44 1 0 | 144 > 3 | 7 34 96 5 1 | 143 > 4 | 0 3 18 16 0 | 37 > -----------+--------------------------+----- > Total | 56 133 164 22 1 | 376 > > > Is the command -mvrepeat- that Philip Ender wrote, appropriate? > > ---------------------------------------------------------------------------- > > In this case, -mvrepeat- would give the same answer as -ttest- using the > paired t-test syntax. I vaguely recall reading that under these > circumstances Student's t-test does surprisingly well with ordinal data with > as few as three categories, but consider using an alternative, such as a > nonparametric test or a modeling command intended for ordered categorical > data. There are several of each from which to choose. In addition > to -ologit- (illustrated below), Stata has user-written commands that don't > rely upon the proportional odds assumption, at least one of which > (-gologit-) allows the -cluster()- option. > > To observe the direction of change and its magnitude, you can either > use -predict- after one of the modeling commands or plot the data using a > graphing command specifically for ordered categorical data. (I've > illustrated using -ordplot-, but be aware that its author, Nick Cox, has > enhanced it and updated it for Stata Release 8 under the name > of -distplot-.) > > Joseph Coveney > > clear > set more off > input byte sco0 byte cou1 byte cou2 byte cou3 byte cou4 byte cou5 > 1 28 18 6 0 0 > 2 21 78 44 1 0 > 3 7 34 96 5 1 > 4 0 3 18 16 0 > end > reshape long cou, i(sco0) j(sco1) > drop if cou == 0 > expand cou > drop cou > signtest sco0 = sco1 > signrank sco0 = sco1 > generate int pid = _n > reshape long sco, i(pid) j(tim) > somersd tim sco, cluster(pid) > ologit sco tim, cluster(pid) > npt_s sco, by(tim) strata(pid) nodetail > version 7: ordplot sco, by(tim) > gllamm sco tim, i(pid) family(binomial) link(ologit) > estimates store A > gllamm sco, i(pid) family(binomial) link(ologit) > estimates store B > lrtest A B, stats > exit > > > * > * For searches and help try: > * http://www.stata.com/support/faqs/res/findit.html > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**st: Re: comparison between a repeated ordinal measures***From:*"Michael Wood" <mwood@hunter.cuny.edu>

**References**:**Re: st: comparison between a repeated ordinal measures***From:*Joseph Coveney <jcoveney@bigplanet.com>

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